You can do it either way, my preference

enter the fixed assets
1234 some street, apt B
>> land
>> buidling cost
>> >> building accumulated depreciation

land is not depreciated

enter the mortgage as a journal entry
debit land, $$$ (half the land value)
debit building cost, $$$$ (half the building value)
debit owner equity draw, $$$$ (personal half land and building)
credit mortgage liability, $$$$$

If you made a down payment it is split the same way
debit land
debit building
debit equity draw
credit bank

When you make a mortgage payment split the payment
interest expense, $$$ (half the interest paid)
equity draw, $$$ (half the interest paid)
mortgage payable, $$ (remaining amount of the payment)